It has been proposed to utilize atmospheric fluidized bed combustors for heating a working fluid in closed-cycle gas turbine power generation systems. They can be readily used to provide a working fluid, e.g., air, at temperatures up to about 1500.degree. by passage of the fluid through tubes contained in a fluidized bed combustion zone operated at 1600.degree. to 1700.degree. F.
The high-temperature medium contained in the fluidized bed is normally generated by combustion of a sulfur-containing particulate carbonaceous fuel such as sulfur-containing coal. It is abrasive and corrosive. Corrosive conditions exist, in part, due to sulfur dioxide generated as a consequence of combustion, and, in part, by the existence of zones of reducing atmosphere. Reducing atmosphere zones form in crevices where heat exchange tubes pass through the side walls of the fluidized bed enclosure. There, fluids stagnate and become more corrosive than the dynamic zones within the fluidized bed. There exists, therefore, a need to provide fluidized bed combustors where corrosion problems due to fluid stagnation are eliminated.